One known way of controlling the position of a moving member which is rotatable about an axis or which is translatable in a plane (e.g. a flap or the like disposed in an air duct in a heater or air conditioner installation) is direct control by means of a cable having one end connected to the member to be moved, and its other end connected to control means such as a cursor, a lever, or the like. However, this type of control must be associated with brake means for keeping the moving member in the selected position in spite of other forces which may be exerted thereon (forces due to the flow of air past the flap, due to vibrations, etc.).
Another known way of controlling the position which requires less force than a cable-and-brake arrangement consists in moving the moving member by means of an actuator jack (generally an on/off actuator) which is connected to a source of fluid pressure and to an exhaust via a selector valve or switch under user control. This technique can be used to obtain either a continuous displacement of the moving member between two extreme positions, or else to obtain a step-by-step displacement of the moving member which then occupies a set of predetermined positions. In the latter case, multiposition actuators are generally used having cylinders comprising a plurality of chambers delimited by deformable membranes, and having a plurality of inlet orifices for feeding fluid under pressure to respective ones of the actuator chambers.
Such actuators are relatively expensive, and only limited numbers of positions are available for moving members under their control.
Preferred embodiments of the present invention provide a fluid flow selector valve for supplying fluid under pressure to an actuator for step-by-step control of a moving member between predetermined positions, but capable of using an ordinary on/off type of actuator and without the number of available positions being limited by the actuator.